This application claims the priority of Japanese Patent Application No. 10-14980 filed on Jan. 9, 1998, Nos. 10-33776 and 10-33777 filed on Jan. 30, 1998, Nos. 10-38170 and 10-38171 filed on Feb. 4, 1998 and No. 10-54421 filed on Feb. 18, 1998 which are incorporated herein by reference.
The present invention relates to an electronic endoscope apparatus, and more particularly to structure of an electronic endoscope apparatus for forming a still image through the use of an all-pixel reading system which reads out all pixels accumulated on an image-pickup device.
In an electronic endoscope apparatus, for example, CCD (Charge Coupled Device) is used as a solid image-pickup device, and this CCD is structured so as to obtain an image signal (video signal) by reading out charge accumulated in units of pixels by a photoelectric conversion device. In, for example, a simultaneous type electronic endoscope apparatus, color filters are arranged in units of pixels on the top surface of the foregoing CCD to thereby obtain a color image.
FIG. 16 shows an arrangement state for the foregoing color filters, and Mg (magenta) and Cy (cyan) pixels are arranged on, for example, an even line, and G (green) and Ye (yellow) pixels are arranged on an odd line on a picked-up surface of CCD 1 as shown. In this CCD 1, accumulated charge (pixel signal) in units of pixels is to be obtained through these color filters.
According to a conventional color difference line sequential mix reading (pixel mix reading) system, accumulated charges of pixels on the upper and lower lines are added and mixed to be read out. For example, during first exposure, video signals of such Odd field as a mixed signal of 0-line and 1-line, a mixed signal of 2-line and 3-line, . . . are read out, and during the second exposure, video signals of such even field as a mixed signal of 1-line and 2-line, a mixed signal of 3-line and 4-line, . . . are read out. Therefore, two lines of mixed signals of CCD 1 become one line of signals of field image, and one odd or even field of data are to be obtained by one exposure.
FIG. 17 shows an operation of signals read out from the foregoing CCD 1, and in an electronic endoscope apparatus, an odd field and an even field are formed on the basis of the O (Odd)/E (Even) signal (field signal) for each {fraction (1/60)} second (vertical synchronizing period) as shown in FIG. 17(A). Therefore, as shown in FIG. 17(B), signals are accumulated in accumulation (exposure) time T of an electronic shutter during the foregoing period of {fraction (1/60)} second, and the accumulation mixed signal is read out during the next {fraction (1/60)} second period. As a result, as shown in FIG. 17(C), an odd field signal, and an even field signal are to be obtained, and for example, the (nxe2x88x921)th odd field signal becomes mixed signals of (0+1)line, (2+3)line, (4+5)line . . . which are shown on the left of FIG. 16, and the n-th even field signal becomes mixed signals of (1+2)line, (3+4)line, . . . which are shown on the right of FIG. 16.
These odd field signals and even field signals are interlace scanned to be formed as an one-frame image, and this image is displayed as a moving image on a monitor. Also, in the endoscope apparatus, a freeze switch is arranged in the operating unit, and when this freeze switch is depressed, a still image at the time is formed and displayed.
In the foregoing simultaneous type electronic endoscope apparatus, however, there is a time lag of {fraction (1/60)} second between those odd field image and even field image which are used to form the one-frame image as shown in the foregoing FIG. 17(C), and if there is a shake of the endoscope itself, a movement of the object to be observed or the like during this period of time, there is the problem that the image quality (resolution, color shift, etc.) will be deteriorated when the still image is displayed. In other words, in the case of a moving image, it is often better to faithfully reproduce the movement and the like of the subject conversely by the foregoing mix reading system in the CCD 1, but in the case of a still image, the resolution will be deteriorated.
Also, in the electronic endoscope apparatus, an electronic shutter function for changing the accumulation time of a signal is frequently adopted, and by the use of the electronic shutter, it is possible to improve the image quality if the accumulation time is made shorter in a light place at a short distance or the like. As shown in FIG. 17, however, there is a time lag of {fraction (1/60)} second between two accumulation (exposure) for forming an one-frame image, and in a still image, there is the inconvenience that the effect of shortened accumulation time is not sufficiently exhibited.
The present invention has been achieved in the light of the foregoing problems, and is aimed to supply an electronic endoscope apparatus capable of forming a still image with high image quality by reading out all pixels obtained through an image-pickup device by one exposure, and faithfully reproducing the movement concerning a moving image.
Another object is to prevent, in the foregoing electronic endoscope apparatus, any incomplete image from being displayed or the screen from being blurred when switching from a moving image to a still image.
Still another object is to stabilize, in the foregoing electronic endoscope apparatus, black level clamping treatment when a still image is selected, and to prevent the image quality from being deteriorated.
In order to achieve the foregoing object, an electronic endoscope apparatus according to a first invention comprises: an image-pickup device having a plurality of color filters arranged in units of pixels; light shielding means for intercepting illumination light so that pixel signals for a predetermined period of time are not accumulated on this image-pickup device; and switching means for switching driving control for both a pixel mix reading system, which mixes pixels accumulated on the foregoing image-pickup device between upper and lower horizontal lines to output from the image-pickup device, and a all-pixel reading system, which reads out signals of all pixels accumulated on the foregoing image-pickup device by one exposure through the use of a light shielding period set by the foregoing light shielding means.
In the foregoing, there can be provided control means for forming a moving image using the foregoing pixel mix reading system and a still image using the foregoing all-pixel reading system while controlling the foregoing switching means.
Also, the foregoing first invention is preferably structured by including: an image-pickup device driving circuit for controlling so as to read out, concerning all pixel signals accumulated on the foregoing image-pickup device by one exposure, image signals on either an odd line or an even line first, and next to read out image signals on the remaining line; a memory for storing, at the execution of the foregoing all-pixel reading system, image signals on the foregoing odd line obtained from the image-pickup device and image signals on the foregoing even line; a phase adjustment memory for adjusting phase, at the execution of the foregoing all-pixel reading system, between image signals on a predetermined line previously stored in the foregoing memory and image signals on the other line; a mixing circuit for forming a still image signal by mixing pixel signals of the foregoing odd line and the foregoing even line during the same exposure which have been read out from the foregoing each memory; and an image switching circuit for directly inputting a moving image signal of the pixel mix reading system outputted from the foregoing image-pickup device to switch either this moving image signal or the still image signal outputted from the foregoing mixing circuit on the basis of the operation of a freeze switch.
According to the foregoing structure, the pixel mix reading system has been selected at the output of the image-pickup device, during, for example, a normal operation, a pixel mixed signal read out from the image-pickup device in the same manner as before is directly supplied to the image switching circuit, and a pixel mixed signal outputted through this image switching circuit is subjected to the signal processing for a moving image. Thus, when the freeze switch is depressed, it is switched to the all-pixel reading system to thereby form a still image.
As regards, for example, charge accumulated by exposure (arbitrary exposure time) within a predetermined (assumed to be a first one) {fraction (1/60)} second period (vertical synchronizing period), the odd line of the image-pickup device (CCD) is read out during the second period ({fraction (1/60)} second) (read out from the transfer line) to be stored in a predetermined memory, and the remaining even line is read out during the third (next exposure time) period to be also stored in a predetermined memory. In order to enable this even line to be read out, the light source light during the foregoing second period is intercepted by the light shielding means.
In other words, when charge for the next exposure is accumulated as before during the second period in which the accumulated charge on the foregoing odd line is successively read out, the remaining even line cannot be read out. Therefore, according to the present invention, the light output within the second period is left out to read out accumulated charge on the even line during the third period. Thus, the signals for all pixels of the image-pickup device obtained by one exposure can be read out.
Next, a video signal on, for example, the odd line first stored in the foregoing memory is further stored in the phase adjustment memory, delayed by {fraction (1/60)} second, and thereafter, a pixel mixing process is performed between odd line data and even line data by the mixing circuit. More specifically, as a result, this pixel mixing process forms a similar signal to the pixel mix reading system at the output of an image-pickup device which is performed at the output of a signal from the image-pickup device, but is distinguished from pixel mix reading system at the output of an image-pickup device in terms of pixel mixing in accordance with the information obtained by one exposure.
Thus, this pixel mixing signal forms video signals for the odd field and the even field, and a still image is displayed on the basis of these video signals. Accordingly, the still image is to be formed on the basis of signals of all pixels obtained by one exposure, thus becoming a high-quality image.
An electronic endoscope apparatus according to a second invention is constituted by including, in the foregoing first invention, delay means for delaying moving image data obtained by the foregoing pixel mix reading system by a predetermined period, and a signal processing circuit for forming a moving image signal on the basis of moving image data obtained through this delay means.
This second invention eliminates the inconvenience which occurs when the operation described in the first invention is performed. More specifically, during a normal operation in which the freeze switch is not depressed, the pixel mix reading system at the output of an image-pickup device has been selected, and pixels of two horizontal lines read out from the image-pickup device are mixed and outputted in the same manner as before. On switching from the moving image to a still image, however, since the illumination light is intercepted, and it is switched to the all-pixel reading system, image processing is performed through moving image data which are a half the ordinary one in, for example, one frame immediately before the still image is displayed, thus causing such a phenomenon that an incomplete image (image having half luminance and improper color) is displayed. Thus, according to the second invention, the moving image data are delayed as a whole by processing time corresponding to one frame using, for example, the foregoing delay memory in such a manner that any moving image is not formed through image data obtained during intercepted light. In this way, the display of any improper image caused on switching from the moving image to a still image is prevented.
A third invention comprises: control means for forming a moving image using the foregoing pixel mix reading system and a still image using the foregoing all-pixel reading system; and a memory for storing at least the foregoing moving image data, and the foregoing control means inhibits still image data read out from the foregoing image-pickup device when the foregoing all-pixel reading system is selected from being written in the foregoing memory as moving image data. In other words, a write-inhibit signal is outputted to a memory, in which, for example, moving image data are stored, for controlling so that the still image data obtained using the all-pixel reading system are prevented from being written in the foregoing memory as moving image data. According to this invention, the immediately preceding moving image data already obtained are used again in place of the incomplete data, and the display of an improper image caused on switching to the still image is prevented as in the case of the foregoing second invention.
A fourth invention comprises: control means for forming a moving image using the foregoing pixel mix reading system and a still image using the foregoing all-pixel reading system; and a memory for storing at least the foregoing moving image data, and the foregoing control means sets a write-inhibit period to prevent still image data read out from the foregoing image-pickup device when the foregoing all-pixel reading system is selected from being written in the foregoing memory as moving image data. The foregoing control means also continuously reads out the data in either the odd field or the even field which have been already written in the memory as frame data during the foregoing write inhibit period.
This fourth invention controls, as in the case of the foregoing third invention, so as not to write still image data obtained using the all-pixel reading system in a memory in which moving image data are stored, and continuously reads out, for example, only odd field data. This prevents the display of any improper image caused on switching to a still image, and odd (or even) field data are continuously read out at least twice (for one frame), whereby blurring of an image can be suppressed. More specifically, as data for substituting as the still image data, the immediately preceding data can be also used again for both odd field and even field, but in this case, the image is displayed through data which are temporally inverted, and therefore, the display screen will be blurred if, for example, the object moves from side to side. Thus, according to the invention, the field data which are temporally inverted are not used, but only either odd or even data are read out to display the image for eliminating the blurred screen.
A fifth invention has the foregoing image-pickup device, light shielding means, and switching means for switching driving control for both systems, and comprises: a clamping circuit for clamping an image signal outputted from the foregoing image-pickup device through a clamp signal; switching control means for controlling so as to extract a black information signal in the moving image signal obtained by the pixel mix reading system at the output of the foregoing image-pickup device even when the foregoing all-pixel reading system is selected; and a signal processing circuit for forming a clamp signal from the black information signal obtained by the control of this switching control means to feed back this clamp signal to the foregoing clamping circuit.
Generally, in the image processing in an electronic endoscope apparatus, a clamping process for causing black levels to coincide for each horizontal scanning period is performed as well known, but in the clamping process for the foregoing still image (all-pixel reading system), since the displaying process is performed through image data once stored in the memory, the clamp signal is formed on the basis of old data. Therefore, during shifting from the still image to the moving image, the black level of the signal is greatly changed, and in this case, the reproducibility of color is deteriorated. In the fifth invention, however, a black information signal of the current moving image signal is extracted even when a still image is being processed for display, and a clamp signal is formed on the basis of this black information signal for clamping process. Therefore, the great fluctuation of the black level will be eliminated, and it becomes possible to display a good image even when the display is switched from a still image to a moving image.
An electronic endoscope apparatus according to a sixth invention has, as in the foregoing second invention, delay means for delaying moving image data obtained by the foregoing pixel mix reading system by a predetermined period, and is characterized by comprising switching control means for directly inputting a moving image signal obtained by the foregoing pixel mix reading system without passing through the foregoing delay means, and controlling so as to extract a black information signal in the moving image signal.
In the foregoing second invention, the moving image data are delayed as a whole by processing time corresponding to one frame by means of the delay memory so as to prevent any moving image from being formed through the image data obtained when light is intercepted. In the clamping process for the moving image in this case, however, the image data which have been stored once in the delay memory are used for display processing, and therefore, the black level will be determined on the basis of the old data although the same is applicable to the still image. Thus, according to the invention, apart from a processing signal for the moving image (or still image), the black information signal in the current moving image signal directly outputted from the image-pickup device is extracted to perform the clamping process on the basis of the black information signal. Therefore, the great fluctuation of the black level due to time lag is eliminated, and it becomes possible to display a good image when the moving image is selected or even when the display is switched from the still image to the moving image.